x86/process: Allow runtime control of Speculative Store Bypass
authorThomas Gleixner <tglx@linutronix.de>
Sun, 29 Apr 2018 13:21:42 +0000 (15:21 +0200)
committerThomas Gleixner <tglx@linutronix.de>
Thu, 3 May 2018 11:55:50 +0000 (13:55 +0200)
commit885f82bfbc6fefb6664ea27965c3ab9ac4194b8c
tree513fe3316a1be1de813ee01a90be689f3e542365
parentb617cfc858161140d69cc0b5cc211996b557a1c7
x86/process: Allow runtime control of Speculative Store Bypass

The Speculative Store Bypass vulnerability can be mitigated with the
Reduced Data Speculation (RDS) feature. To allow finer grained control of
this eventually expensive mitigation a per task mitigation control is
required.

Add a new TIF_RDS flag and put it into the group of TIF flags which are
evaluated for mismatch in switch_to(). If these bits differ in the previous
and the next task, then the slow path function __switch_to_xtra() is
invoked. Implement the TIF_RDS dependent mitigation control in the slow
path.

If the prctl for controlling Speculative Store Bypass is disabled or no
task uses the prctl then there is no overhead in the switch_to() fast
path.

Update the KVM related speculation control functions to take TID_RDS into
account as well.

Based on a patch from Tim Chen. Completely rewritten.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
arch/x86/include/asm/msr-index.h
arch/x86/include/asm/spec-ctrl.h
arch/x86/include/asm/thread_info.h
arch/x86/kernel/cpu/bugs.c
arch/x86/kernel/process.c